U.S. patent number 6,479,421 [Application Number 09/457,802] was granted by the patent office on 2002-11-12 for process for making, and use of, anionic clay materials.
This patent grant is currently assigned to Intercat, Inc.. Invention is credited to Albert A. Vierheilig.
United States Patent |
6,479,421 |
Vierheilig |
November 12, 2002 |
Process for making, and use of, anionic clay materials
Abstract
Anionic clay compounds such as hydrotalcite-like compounds can
be made by a process wherein a non-hydrotalcite-like compound (or a
hydrotalcite-like compound) are heat treated and then hydrated to
form hydrotalcite-like compounds having properties (e.g..,
increased hardness and/or density) that differ from those of
hydrotalcite-like compounds made by prior art methods wherein
non-hydrotalcite-like compounds (or hydrotalcite-like compounds)
are not similarly heat treated and hydrated to form such
hydrotalcite-like compounds.
Inventors: |
Vierheilig; Albert A.
(Savannah, GA) |
Assignee: |
Intercat, Inc. (Sea Girt,
NJ)
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Family
ID: |
25496264 |
Appl.
No.: |
09/457,802 |
Filed: |
December 9, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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955017 |
Oct 20, 1997 |
6028023 |
|
|
|
Current U.S.
Class: |
502/84; 502/80;
502/85 |
Current CPC
Class: |
B01J
21/16 (20130101); B01J 21/10 (20130101); B01J
23/002 (20130101); B01J 23/007 (20130101); C01F
7/005 (20130101); C10G 11/02 (20130101); C01B
13/14 (20130101); C01P 2002/22 (20130101); C01P
2002/32 (20130101); C01P 2006/21 (20130101); B01J
2523/00 (20130101); C01P 2002/72 (20130101); C01P
2006/10 (20130101); B01J 2523/00 (20130101); B01J
2523/22 (20130101); B01J 2523/31 (20130101); B01J
2523/3712 (20130101); B01J 2523/55 (20130101); B01J
2523/00 (20130101); B01J 2523/22 (20130101); B01J
2523/31 (20130101) |
Current International
Class: |
C01B
13/14 (20060101); B01J 21/10 (20060101); B01J
23/00 (20060101); B01J 21/00 (20060101); B01J
21/16 (20060101); C01F 7/00 (20060101); B01J
021/16 () |
Field of
Search: |
;502/80,84,85 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Walter T. Reichle, "Synthesis of Anionic Clay Minerals (Mixed Metal
Hydroxides, Hydrotalcite)," Solid State Ionics, 22, pp. 135-141
(1996). .
Miyata, "Physico-Chemical Properties of Synthetic Hydrotalcites in
Relation to Composition," Clays and Clay Minerals, vol. 28, No. 1,
pp. 50-56 (1980). .
Pausch, "Syntheses of Disordered and Al-Rich Hydrotalcite
Compounds," vol. 14, No. 5, pp. 507-510 (1986)..
|
Primary Examiner: Silverman; Stanley S.
Assistant Examiner: Ildebrando; Christina
Attorney, Agent or Firm: Olstein; Elliot M. Lillie; Raymond
J.
Parent Case Text
This patent application is a continuation patent application of
U.S. patent application Ser. No. 08/955,017 filed Oct. 20, 1997 now
U.S. Pat. No. 6,028,023.
Claims
Thus, having disclosed this invention, what is claimed is:
1. A process for making an HTL compound having an XRD pattern which
has 2 theta peak positions that are nearly identical to those found
in ICDD card 35-965, comprising: (a) preparing a reaction mixture
comprising an aluminum-containing compound, a magnesium-containing
compound, a cerium-containing compound, and a vanadium-containing
compound under conditions such that a product obtained from the
reaction mixture is an HTL compound whose XRD pattern is not that
of ICDD card 35-965; (b) converting said HTL compound whose XRD
pattern is not that of ICDD card 35-965 into a microspheroidal form
suitable for use as an SOx sorbent; (c) heat treating said HTL
compound whose XRD pattern is not that of ICDD card 35-965 at a
temperature of from 300.degree. C. to 850.degree. C. to obtain a
collapsed, heat treated HTL compound whose XRD pattern is not that
of ICDD card 35-965; and (d) hydrating said collapsed, heat
treated, HTL compound whose XRD pattern is not that of ICDD card
35-965 to obtain an HTL compound having an XRD pattern which has 2
theta peak positions that are nearly identical to those found in
ICDD card 35-965, and which is suitable for use as an SOx
sorbent.
2. The process of claim, wherein said HTL compound whose XRD
pattern is not that of ICDD card 35-965 is heat treated at a
temperature of from about 400.degree. C. to about 500.degree.
C.
3. The process of claim 2 wherein said HTL compound whose XRD
pattern is not that of ICDD card 35-965 is heat treated at a
temperature of about 450.degree. C.
Description
BACKGROUND OF THE INVENTION
This invention is generally concerned with methods of making
anionic clays. Such clays are characterized by crystalline
structures that consist of positively charged layers that are
separated by interstitial anions and/or water molecules. The
positively charged layers are often comprised of metal hydroxides
of divalent metal cations (e.g., Mg.sup.2+, Ca.sup.2+, Zn.sup.2+,
Mn.sup.2+, Co.sup.2+, Ni.sup.2+, Sr.sup.2+, Ba.sup.2+ and Cu.sup.+)
and trivalent metal cations (e.g., Al.sup.3+, Mn.sup.3+, Fe.sup.3+,
Co.sup.3+, Ni.sup.3+, Cr.sup.3+, Ga.sup.3+, B.sup.3+, La.sup.3+ and
Gl.sup.3+). The interstitial anions are usually NO.sub.3 --, OH--,
Cl--, Cr--, I--, CO.sub.3.sup.2-, SO.sub.4.sup.2-,
SIO.sub.3.sup.2-, HPO.sub.3.sup.2-, MnO.sub.4 --,
HGaO.sub.3.sup.2-, HVO.sub.4.sup.2-, ClO.sub.4 --, BO.sub.3.sup.2-,
monocarboxylates (e.g., acetate) and dicarboxylates (e.g.,
oxalate), alkyl sulphonates (e.g., lauryl sulphonate) and various
combinations thereof.
Therefore, anionic clays are further subdivided according to the
identity of the atoms that make up their crystalline structures.
For example, anionic clays in the
pyroaurite-sjogrenite-hydrotalcite group are based upon
brucite-like layers (wherein magnesium cations are octahedrally
surrounded by hydroxyl groups) which alternate with interstitial
layers of water molecules and/or various anions (e.g., carbonate
ions). When some of the magnesium in a brucite-like layer is
isomorphously replaced by a higher charged cation, e.g., Al.sup.3+,
then the resulting Mg.sup.2+ --Al.sup.3+ --OH layer gains in
positive charge. Hence, an appropriate number of interstitial
anions, such as those noted above, are needed to render the overall
compound electrically neutral.
The literature also teaches that as the concentration of Al.sup.3+
increases in a Brucite-type lattice, a reduction of the lattice
parameter known as "a", takes place. The lattice parameter known as
"c" also is reduced. The reduction in lattice parameter, a, is due
to the smaller, plus three charged, Al.sup.3+ ions substituting for
the larger, plus two charged Mg.sup.2+ ions. This higher charge
causes increased coulombic forces of attraction between the
positive charged Brucite-type layer and the negative interlayer
ions--thus giving rise to a decrease in the size of the interlayer
itself.
Natural minerals that exhibit such crystalline structures include,
but by no means are limited to, pyroaurite, sjogrenite,
hydrotalcite, stichtite, reevesite, eardleyite, mannaseite,
barbertonite and hydrocalumite. The chemical formulas for some of
the more common synthetic forms of anionic clays would include:
[Mg.sub.6 Fe.sub.2 (OH).sub.16 ]CO.sub.3. 4H.sub.2 O, [Mg.sub.6
Al.sub.2 --(OH).sub.16 ]CO.sub.3.4H.sub.2 O, [Mg.sub.6 Cr.sub.2
(OH).sub.16 ]CO.sub.3.4H.sub.2 O, [Ni.sub.6 --Fe.sub.2 (OH).sub.16
]C.sub.3.4H.sub.2 O, [Ni.sub.6 Al.sub.2 (OH).sub.16
]CO.sub.3.4H.sub.2 O, [Fe.sub.4 Fe.sub.2 (OH).sub.12
]CO.sub.3.#H.sub.2 O, [Ca.sub.2 Al (OH).sub.6 ](OH).sub.0.75
--(CO.sub.3).sub.0.125 2.5H.sub.2 O.sub.6 ]OH.6H.sub.2 O, [Ca.sub.2
Al--(OH).sub.6 ]OH.3H.sub.2 O, [Ca.sub.2 Al(OH).sub.6 ]OH.2H.sub.2
O, [Ca.sub.2 Al--(OH).sub.6 ]OH, [Ca.sub.2 Al(OH).sub.6 ]Cl.sub.2
H.sub.2 O, [Ca.sub.2 Al(OH).sub.6 ]0.5CO.sub.3 2.5H.sub.2 O,
[Ca.sub.2 Al(OH).sub.6 ]0.5SO.sub.4.3H.sub.2 O, [Ca.sub.2
--Fe(OH).sub.6 ]0.5SO.sub.4.3H.sub.2 O, [(Ni, Zn).sub.6 Al.sub.2
(OH).sub.16 ]CO.sub.3.4H.sub.2 O, [Mg.sub.6 (Ni, Fe).sub.2
(OH).sub.16 ](OH).sub.2.2H.sub.2 O, [Mg.sub.6 Al.sub.2 (OH).sub.16
--](OH).sub.2.4H.sub.2 O, [(Mg.sub.3 Zn.sub.3)al.sub.2 (OH).sub.16
]CO.sub.3.4H.sub.2 O, [Mg.sub.6 Al.sub.2 (OH).sub.16
]SO.sub.4.xH.sub.2 O, [Mg.sub.6 Al.sub.2 (OH).sub.16
](NO.sub.3).sub.2.x--H.sub.2 O, [Zn.sub.6 Al.sub.2 (OH).sub.16
]CO.sub.3.xH.sub.2 O, [Cu.sub.6 Al.sub.2 (OH).sub.16-
]CO.sub.3.xH.sub.2 O, [Cu.sub.6 Al.sub.2 (OH).sub.16
]SO.sub.4.xH.sub.2 O and [Mn.sub.6 Al.sub.2- (OH).sub.16
]CO.sub.3.xH.sub.2 O, wherein x has a value of from 1 to 6.
Those skilled in this art also will appreciate that anionic clays
are often referred to as "mixed metal hydroxides." This expression
derives from the fact that, as noted above, positively charged
metal hydroxide sheets of anionic clays may contain two metal
cations in different oxidation states (e.g., Mg.sup.2+ and
Al.sup.3+). Moreover, because the XRD patterns for so many anionic
clays are similar to that of the mineral known as Hydrotalcite,
Mg.sub.6 Al.sub.2 (OH).sub.16 (CO.sub.3).4H.sub.2 O, anionic clays
also are very commonly referred to as "hydrotalcite-like
compounds." This term has been widely used throughout the
literature for many years (see for example: Pausch, "Synthesis of
Disordered and Al-Rich Hydrotalcite-Like Compounds," Clay and Clay
Minerals, Vol. 14, No. 5, 507-510 (1986). Such compounds also are
often referred to as "anionic clays." Indeed, the expressions
"anionic clay," "mixed metal hydroxides" and "hydrotalcite-like
compounds" are often found very closely linked together. For
example, in: Reichle, "Synthesis of Anionic Clay Minerals (Mixed
Metal Hydroxides, Hydrotalcite)," Solid State Ionics, 22, 135-141
(1986) (at Paragraph 1, page 135) the author states: "The anionic
clays are also called mixed metal hydroxides since the positively
charged metal hydroxide sheets must contain two metals in different
oxidation states. Crystallographically they have diffraction
patterns which are very similar or identical to that of
hydrotalcite (Mg.sub.6 Al.sub.2 (OH).sub.16 (CO.sub.3).4H.sub.2 O);
hence they have also been referred to as hydrotalcites or
hydrotalcite-like." (emphasis added). U.S. Pat. No. 5,399,329 (see
col.1, lines 60-63) contains the statement: "The term
`hydrotalcite-like` is recognized in this art. It is defined and
used in a manner consistent with usage herein in the comprehensive
literature survey of the above-referenced Cavani et al. article."
Hence, for the purposes of the present patent disclosure, applicant
will (unless otherwise stated) use the term "hydrotalcite-like"
compound(s) with the understanding that this term should be taken
to include anionic clays, hydrotalcite itself as well as any member
of that class of materials generally known as "hydrotalcite-like
compounds." Moreover, because of its frequent use herein, applicant
will often abbreviate the term "hydrotalcite-like" with
The methods by which HTL compounds have been made are found
throughout the academic and the patent literature. For example,
such methods have been reviewed by Reichle, "Synthesis of Anionic
Clay Minerals (Mixed Metal Hydroxides, Hydrotalcite)," Solid States
Ionics, 22 (1986), 135-141, and by Cavani et al., CATALYSIS TODAY,
Vol. 11, No. 2, (1991). In the case of hydrotalcite-like compounds,
the most commonly used production methods usually involve use of
concentrated solutions of magnesium and aluminum which are often
reacted with each other through use of strong reagents such as
sodium hydroxide, and various acetates and carbonates. Such
chemical reactions produce hydrotalcite or hydrotalcite-like
compounds which are then filtered, washed, and dried. The resulting
HTL compounds have been used in many ways--but their use as
hydrocarbon cracking catalysts, sorbents, binder materials for
catalysts and water softener agents is of particular relevance to
this patent disclosure.
It also is well known that HTL compounds will decompose in a
predictable manner upon heating and that, if the heating does not
exceed certain hereinafter more fully discussed temperatures, the
resulting decomposed materials can be rehydrated (and, optionally,
resupplied with various anions, e.g., CO.sub.3.sup.=, that were
driven off by the heating process) and thereby reproduce the
original, or a very similar, HTL compound. The decomposition
products of such heating are often referred to as "collapsed," or
"metastable," hydrotalcite-like compounds. If, however, these
collapsed or metastable materials are heated beyond certain
temperatures (e.g., 900.degree. C.), then the resulting
decomposition products of such hydrotalcite-like compounds can no
longer be rehydrated and, hence, are no longer capable of forming
the original hydrotalcite-like compound.
Such thermal decomposition of hydrotalcite-like compounds has been
carefully studied and fully described in the academic and patent
literature. For example, Miyata, "Physico-Chemical Properties of
Synthetic Hydrotalcites in Relation to Composition," Clays and Clay
Minerals, Vol. 28, No. 1, 50-56 (1980), describes the temperature
relationships and chemical identity of the thermal decomposition
products of hydrotalcite in the face of a rising temperature regime
in the following terms: "It is of interest to know the form in
which the Al occurs after thermal decomposition of the hydrotalcite
structure. A sample with x=0.287, hydrothermally treated at
200.degree. C. for 24 hr, was calcined at 300.degree.-1000.degree.
C. in air for 2 hr. After calcination at 300.degree. C., both
hydrotalcite and MgO were detected by X-ray diffraction, but after
calcination at 400.degree.-800.degree. C. only MgO could be
detected. At 900.degree. C. MgO, MgAl.sub.2 O.sub.4, and a trace of
.gamma.-Al.sub.2 O.sub.3 were detected." (emphasis added, for
reasons to be explained in the ensuing portions of this patent
disclosure)
Miyata then goes on to note that: "The crystallite size was smaller
than 50 .ANG. when the sample was calcined below 800.degree. C.
This value was much smaller than that for MgO obtained from pure
Mg(OH).sub.2. On calcination above 800.degree. C., the crystallite
size rapidly increased. The changes of the crystallite size and
lattice parameter a have the same tendency. Consequently, Al
substituting in MgO acts to inhibit crystal growth. If
Al-containing MgO is reacted with water, it should first form
hydrotalcite. Hydrotalcite calcined at 400-800.degree. C. with
x=0.287 was hydrated at 80.degree. C. for 24 hr, and the products
were examined by X-ray powder diffraction. According to Table 7,
hydrotalcite was the only hydrated product detected in samples
calcined at 400-700.degree. C. The lattice parameter a is the same
as that of the original sample. The samples calcined at 800.degree.
C. also formed only hydrotalcite but their lattice parameters are
larger than that of the original sample. According to FIG. 1, the
molar ratio of this product is x=0.235. On the other hand, Al.sub.2
O.sub.3 does not react with water under the above-mentioned
conditions. Therefore, the results suggest that Al enters product
MgO when hydrotalcite is calcined between 400 and 700.degree. C."
(emphasis added)
U.S. Pat. No. 5,459,118 ("the '118 patent") describes the character
of the materials that result from progressively heating
hydrotalcite-like compositions (HTlc's) in a passage running from
col. 4, line 67 to col. 5, line 14. It reads as follows: "The
natural products of calcination or activation in inert gas of a
HTlc is believed to be a spinel. In the range between the
temperature at which HTlc decomposition commences (between
572.degree. and 752.degree. F.) (i.e., between 300.degree. C. and
400.degree. C.) and that of spinel formation (1652.degree. F.)
(i.e., at 900.degree. C.) , a series of metastable phases form,
both crystalline and amorphous. Therefore, the surface area, pore
volume, and structure depend on the temperature of calcination.
Upon calcination, the crystal structure of DHT-4A is decomposed at
about 660.degree. F. (i.e., 349.degree. C.) when water and carbon
dioxide evolved from the structure, and a MgO--Al.sub.2 O.sub.3
solid solution of formula 4.5 MgO.Al.sub.2 O.sub.3 is formed. This
solid solution is stable up to 1472.degree. F. (i.e., 800.degree.
C.) MgO and MgAl.sub.2 O.sub.4 are formed at about 652.degree. F.
(i.e., 900.degree. C.). On the other hand, the solid solution
calcined at less than 1472.degree. F. (i.e., 800.degree. C.) can be
restored in the original structure by hydration." (The underlined
portions of this passage have been added to convert .degree. F. to
.degree. C. in order to more directly compare the teachings of this
reference with other relevant references wherein temperatures are
expressed in .degree. C., again such comparisons will be made in
the next few paragraphs of this patent disclosure)
It might also be noted here that this quotation from the '118
patent is a precise statement of the temperatures at which certain
hydrotalcite decomposition products are described (e.g., spinel,
MgAl.sub.2 O.sub.4, formation taking place at 900.degree. C. when
hydrotalcite is thermally decomposed). This more exact knowledge of
the temperatures at which certain aspects of the decomposition of
hydrotalcite take place, clarifies many other, more general,
statements found in the literature concerning the temperatures at
which certain decomposition products are formed (e.g., statements
concerned with the temperature at which spinel, MgAl.sub.2 O.sub.4,
is formed from a hydrotalcite starting material). That is to say
that many, more general, statements concerning the temperatures at
which various hydrotalcite thermal decomposition products (e.g.,
spinel, MgAl.sub.2 O.sub.4) are formed must be carefully
interpreted. For example, in U.S. Pat. No. 4,889,615 ("the '615
patent") at col. 6, lines 36-43, we find the statement: "Calcining
the Mg/Al hydrotalcites at temperatures greater than 500.degree. C.
gives a mixture of MgO and MgAl.sub.2 O.sub.4, a magnesium
aluminate spinel, a material which has been reported to reduce FCC
regenerator SO.sub.x emissions (see U.S. Pat. No. 4,469,589 (Yoo)
and U.S. Pat. No. 4,472,267 (Yoo)). The activity of the dehydrated
hydrotalcite is, however, significantly different than that
observed for the spinel, MgO, or mixtures of both. No evidence of
MgAl381.sub.2 O.sub.4 (sic) is observed in the regenerated
hydrotalcite indicating that the spinel is not the active
component." (emphasis added)
Thus, in view of the previous, more precise, descriptions of the
temperature of spinel formation (i.e., 900.degree. C.) in the '118
patent, it seems that the more general expression "temperatures
greater than 500.degree. C." used in the '615 patent should not be
taken to mean something like 501.degree. C., but rather should be
taken to mean 900.degree. C., a temperature which is indeed
"greater than 500.degree. C." It also should be noted that the
above-quoted passage recognizes that "spinel is not the active
component" of the materials described in the '615. We note this
point here because it is consistent with applicant's hereinafter
described goal of not making spinel--so that applicant's heat
treated, intermediate products can in fact be hydrated (or
rehydrated) to form hydrotalcite-like compositions.
A similar general statement concerning spinel formation from a
hydrotalcite precursor appears in U.S. Pat. No. 4,458,026. There
(at col. 3, lines 54-56) we find the statement: "Above 600.degree.
C. the resulting metal oxide mixture begins to sinter and lose
surface area, pore volume, as well as form a catalytically inactive
phase (spinel-MgAl.sub.2 O.sub.4) " (emphasis added)
Here again, applicant is of the opinion that the general expression
"Above 600.degree. C." should not be taken to mean something like
601.degree. C., but rather should be taken to mean far enough above
600.degree. C. to form spinel--MgAl.sub.2 O.sub.4 that is to say
900.degree. C., the temperature at which spinel formation from a
hydrotalcite-like compound has been more precisely determined. This
quotation also notes that spinel is "catalytically inactive".
Indeed, one can even find generalized statements about the
temperature of spinel formation that are better interpreted to mean
lower temperature levels. For example, in U.S. Pat. No. 5,114,898
(at col. 4, lines 43-51) we find the statement: "Reichle in J.
Catal. 101, 352 to 359 (1986) has shown that this heating of
hydrotalcite was accompanied by an increase in the surface area
from about 120 to about 230 m.sup.2 /g (N.sub.2 /BET) and a
doubling of pore volume (0.6 to 1.0 cm.sup.3 /g, Hg intrusion).
Further heating to higher temperatures causes lowering of surface
area as well as reactivity. At 1000.degree. C., the formation of
MgO and the spinel phase, MgAl.sub.2 O.sub.4 has been observed."
(emphasis added)
In this case, applicant thinks that the statement "At 1000.degree.
C. the formation of MgO and spinel phase has been observed", is
better taken to mean: spinel is observed at 1000.degree. C. because
spinel (MgAl.sub.2 O.sub.4) forms at 900.degree. C.--rather than
taken to mean: 1000.degree. C. is the temperature of formation of
spinel. Indeed, applicant has by his own experimental work
confirmed that spinel begins to from in HTL compounds at
900.degree. C.
The prior art also has noted that when various anionic clay-forming
ingredients such as hydrotalcite-forming ingredients (e.g.,
magnesium-containing compositions and aluminum-containing
compositions) are mixed under certain prescribed conditions (e.g.,
certain aging times, pH conditions, temperatures, etc.), the
resulting slurry or precipitate materials (e.g., hydrotalcite-like
materials) will exhibit distinct catalytic properties. Hence, many
such production processes are based upon fine tuning of such time,
temperature, pH, etc. conditions in order to obtain maximum amounts
of a given kind of hydrotalcite-like precipitate product.
The slurry and/or precipitate products of such initial chemical
reactions also have been heat treated to obtain various "collapsed"
or "metastable" hydrotalcite materials that have specific catalytic
properties. Such collapsed materials have, for example, been used
as sorbents (and especially SOX sorbents for fluid catalytic and
fixed hydrocarbon cracking processes), hydrocarbon cracking
catalysts, catalyst binders, anion exchangers, acid residue
scavengers and stabilizers for polymers, and even as antacids
intended for use in the context of human medicine.
The prior art also has long recognized that other ingredients such
as compounds containing Ce, V, Fe and Pt can be added to the
original hydrotalcite-forming reaction mixtures so they will appear
as a distinct phase of various solid products created by such
reactions. Dried forms of such anionic clays (e.g., microspheroidal
particles of such hydrotalcite-like compounds used as SO.sub.x
sorbents in fluid catalytic conversion (FCC) processes) also have
been impregnated with solutions of such metals. Moreover, such
metals have even been made a integral part of the crystalline
structure of hydrotalcite-like materials (see, for example, U.S.
Pat. Nos. 5,114,691 and 5,114,898 which teach use of sulfur
oxidizing catalysts made of layered double hydroxide (LDH)
sorbents, e.g., hydrotalcite-like materials that contain metal ions
(e.g., those of vanadium) that replace some or all of the divalent
metals (Mg.sup.2+) or trivalent metals (Al.sup.3+) that form the
layers of the LDH).
Hydrotalcite-like compounds that are used as catalysts also have
been both heat treated and associated with various catalyst binder
or matrix materials. For example, U.S. Pat. No. 4,866,019 (the '019
patent) discloses that hydrotalcite can be heat treated and used in
association with various binder materials. U.S. Pat. No. 5,153,156
teaches a method for making magnesium/aluminum synthetic anionic
clay catalysts by (1) spray drying a slurry of a magnesium aluminum
synthetic clay, (2) making a plasticized mixture of the spray dried
clay with diatomaceous earth and (3) forming, drying and calcining
the resulting plasticized mixture.
The prior art also has long recognized that anionic clay materials
can be used to catalyze certain specific chemical reactions. For
example, U.S. Pat. No. 4,458,026 teaches use of certain heat
treated anionic clay materials as catalysts for converting acetone
to mesityl oxide and isophorone. The anionic clays are given this
catalytic activity by heating them to temperatures ranging from
about 300 to 600.degree. C.
U.S. Pat. No. 4,952,382 teaches a hydrocarbon conversion process
that employs a catalyst composition containing an anionic clay
wherein the anionic clay serves as a sulfur oxides binding
material.
U.S. Pat. No. 4,970,191 teaches use of polymorphic
magnesium-aluminum oxide compositions as catalysts in various base
catalyzed reactions such as alcohol condensation, isomerization of
olefins, etc.
U.S. Pat. No. 4,889,615 discloses a vanadium trap catalyst additive
comprising a dehydrated magnesium-aluminum hydrotalcite.
U.S. Pat. No. 5,358,701 teaches the use of layered double hydroxide
(LDH) sorbents such as hydrotalcite-like materials as SO.sub.2
sorption agents. This reference postulates that the
sulfur-containing gas absorbs into the hydrotalcite structure as
SO.sub.3.sup.2- anions by replacing the gallery CO.sub.3.sup.2-
anions. The absorbed sulfur is thereafter driven off by calcination
at elevated temperatures (500.degree. C. ). The LDH sorbents are
regenerated by hydrolyzing the calcined product, particularly in
the presence of CO.sub.2 or CO.sub.3.sup.2-.
U.S. Pat. No. 5,114,691 teaches removing sulfur oxide from gas
streams using heated layered double hydroxide (LDH) sorbents having
metal-containing: oxoanions incorporated into the galleries of the
LDH structures.
U.S. Pat. No. 4,465,779 teaches catalytic cracking composition
comprising a solid, cracking catalyst and a diluent containing a
magnesium compound in combination with a heat-stable metal
compound.
U.S. Pat. No. 5,426,083 teaches catalytic use of a collapsed
composition of microcrystallites comprised of divalent metal ions,
trivalent ions, vanadium, tungsten or molybdenum.
U.S. Pat. No. 5,399,329 teaches making hydrotalcite-like materials
by preparing a mixture of magnesium (divalent cation) to aluminum
(trivalent cation) in a molar ratio between 1:1 and 10:1, and in a
mono carboxylic anion to aluminum (trivalent cation) molar ratio
between 0.1:1 to 1.2:1. The process involves reacting a mixture
comprising magnesium and aluminum cations and mono carboxylic
anions in an aqueous slurry having a temperature of at least
40.degree. C. and a pH of at least 7. Generally speaking, a given
synthesis of a HTL compound by any of the methods taught in these
patents was considered a success when the product of its chemical
synthesis reaction (slurries typically were heated and/or pressured
to form a final dry product or precipitate) produces a given HTL
compound having an x-ray diffraction pattern which reasonably
resembles that of a given card in the files of the International
Center for Diffraction Data ("ICDD").
In summarizing the prior art, it might be said that most methods
that have been employed to produce anionic clay compounds, and
especially hydrotalcite-like, anionic clay compounds, usually
involve precipitation or slurry drying of a hydrotalcite-like
product, washing and, optionally, heat treatment of the resulting
dried slurry, or precipitated, composition. Once made, these HTL
compounds, or their thermal decomposition products, have been
employed as catalysts (e.g., as vanadium passivators, SO.sub.x
additives, aldol condensation catalysts, water softening agents,
and even medicines).
SUMMARY OF THE INVENTION
Applicant's contribution to this art has been to discover certain
hereinafter described methods, whereby HTL compounds can be
produced from compounds that do not exhibit HTL structures (e.g.,
as determined by their XRD patterns), but which do exhibit HTL
structures upon being activated by the processes of this patent
disclosure. Applicant also has discovered certain novel methods
whereby anionic clays in general and hydrotalcite-like compounds in
particular can be given certain attributes (increased hardness,
density, etc.) that make such compounds better suited for uses
where these attributes are desirable, e.g., as sorbents for various
chemical species--but especially SO.sub.x sorbents--and especially
those SO.sub.x sorbents (and binder materials) used in FCC units,
as hydrocarbon catalysts, as water softening agents, etc.
Again, those compounds generally described as "anionic clays" in
the literature, and especially hydrotalcite, and HTL anionic clay
compounds, will be collectively referred to as "HTL compounds" for
the purposes of this patent disclosure. More specifically this
invention involves formation of hydrotalcite-like compounds by
certain novel production methods and the use, of certain formed
shapes (microspheroidal particles, extrudates, pellets) containing
those hydrotalcite-like compounds produced by applicant's
processing techniques. For example, these formed shapes (e.g.,
microspheroidal particles, pellets, extrudates, etc.) for certain
specific catalytic uses (e.g., FCC operations, SO.sub.x sorption,
water softener regeneration agents, etc.). Hence, the HTL compounds
of this patent disclosure may constitute part of (or even all of) a
given catalyst particle, pellet, extrudate, etc. By way of example
the HTL compounds of this patent disclosure may be associated with
various binder or matrix forming materials known to the catalyst
making art. Indeed, the HTL compounds of this patent disclosure may
be used as catalysts per se (e.g., as hydrocarbon cracking
catalysts), as SO.sub.x binding agents, or as catalyst binder
materials for other catalyst materials. Hence, for the purposes of
this patent disclosure the term "catalyst" should be taken to mean
not only those HTL compounds that have catalytic or SO.sub.x
binding activity in their own right, but also those HTL compounds
that are used as binders, matrices and/or carriers for other
catalytically active compounds (e.g., binders for metallic,
SO.sub.x oxidation catalysts such as compounds containing platinum,
cerium and vanadium). These applications are all related to the
fact that the HTL compounds produced by applicant's methods can,
among other ways, be characterized by their resistance to
mechanical stresses and, hence, by their ability to function in the
severe environments associated with many chemical reactions.
Applicant's overall invention is primarily based upon a two step
"activation" procedure that is generally comprised of heat treating
and then hydrating certain hereinafter described
hydrotalcite-producing, precursor compounds. This two step process
may, in some cases, be augmented by an additional, but purely
optional, heat treatment step (which may be referred to as Step 3
of applicant's process). These heat treated compounds may be
thought of "collapsed" or "metastable," HTL compound-forming
materials.
Applicant's invention has two general embodiments. The first
embodiment is a method for producing HTL compounds (e.g., anionic
clay compounds, hydrotalcite per se, and various hydrotalcite-like
compounds) from compounds that do not possess the structural
characteristics of HTL compounds. The manner by which this first
embodiment of applicant's invention differs from prior art methods
for making similar HTL compounds is that applicant's initial HTL
synthesis is carried out using those ingredients and those reaction
conditions which are such that they do not directly produce
compounds having a HTL structure, but rather produce compounds that
exhibit a HTL structure only after experiencing applicant's
hereinafter described activation process. Hence, in the first
embodiment of this invention, an actual XRD determination that the
product of applicant's initial slurry or precipitation synthesis
reaction does not produce a compound having an XRD pattern that
reasonably resembles that of a compound having the proper
ingredient atoms (e.g., those of magnesium, aluminum, oxygen and
hydrogen in the case of HTL compounds) on file with the ICDD could
be an optional step in applicant's overall process.
It also should be specially noted, however, that applicant's
synthesis products may well include "amorphous" (non-crystalline)
materials as well as non-HTL, crystalline phases--and combinations
thereof. Indeed, the term "amorphous" as used herein could include
(1) crystalline phases which have crystallite sizes below the
detection limits of conventional x-ray diffraction techniques, (2)
crystalline phases which have some significant degree of ordering,
but which lack a crystalline diffraction pattern due to dehydration
or dehydroxilization (such as in layered aluminosilicates) , and
(3) true amorphous materials which may exhibit short range order,
but no long- range order, such as, for example, silica and borate
glasses.
Whatever their physical form (crystalline or amorphous), these
precursor, synthesis reaction products may be subjected to some
form of "low temperature" (i.e., "low temperature" may be taken to
mean less than about 250.degree. C., for the purposes of this
patent disclosure) drying process before they undergo the heat
treatment aspect of applicant's activation process. Such a low
temperature drying process also may include the physical formation
of those powders, pellets, beads, extrudates, microspheroidal
spheres or granule forms of these reaction product materials that
may be required (or desired) for use of these materials as
catalysts, sorbents, ion exchange agents, etc. This drying step
should, however, be considered "optional" because the most
fundamental version of the first embodiment of applicant's
invention could go directly to its heat treatment step.
This heat treatment step involves heating applicant's synthesis
reaction products to a "medium temperature" (i.e., a temperature in
the range of about 300.degree. C. to about 850.degree. C.). This
heat treatment may be carried out for widely varying periods of
time (e.g., from for about 0.1 to about 24.0 hours. This
300.degree. C.-850.degree. C. heat treatment step may generally be
referred to as Step 1 of applicant's overall "activation" process.
It is more preferred, however, that Step 1 be conducted at a
temperature on the low-end of this 300.degree. C.-850.degree. C.
range. This treatment may be carried; out at some preferred
temperature (e.g., 450.degree. C.) or at different temperatures in
this 300.degree. C. to 850.degree. C. range. Step 1, medium
temperature, heat treatments in the range of about 400.degree. C.
to about 500.degree. C. are, however, highly preferred.
Temperatures at the upper end of applicant's
300.degree.-850.degree. C. range, such as temperatures ranging from
about 700.degree.-850.degree. C., are less preferred since various
less desirable phases (hereinafter more fully described) may result
from heating applicant's precursor, synthesis reaction products to
such levels. The formation of these less desirable phases may
diminish the precursor material's potential to form maximum amounts
of the HTL-containing phases that are the object of applicant's
processes.
These higher temperatures also are less preferred because they come
dangerously close to the 900.degree. C. temperature at which a
particularly undesirable material--namely, spinel (MgAl.sub.2
O.sub.4) begins to form. Again, applicant regards spinel formation
as "anathema" to this process because spinel can not be rehydrated.
This is not to say however that any other material, e.g., MgO, that
be present in such a system at temperatures at or above 900.degree.
C., can not be employed for applicant's purposes. For example, if
applicant's hydrotalcite-like starting material is converted into
spinel (MgAl.sub.2 O.sub.4) it becomes useless for applicant's
purposes; if, however, applicant's starting material is converted
into MgO, it still may be useful (e.g., as an SO.sub.x sorbent
agent).
In any event, temperatures of 900.degree. C. or higher can be
regarded as "high temperatures" for the purpose of this patent
disclosure and they are to be avoided as far-as possible. This
admonition also is consistent with the teachings and spirit of the
literature. That is to say that nowhere does the literature even
remotely suggests that spinel can be reversibly hydrated into any
other phase at ambient temperatures. By way of sharp contrast with
this, the literature teaches that HTL compounds such as
applicant's, very decidedly possess the characteristic of
rehydratability.
The literature also teaches that the basic structural building
block of HTL, the brucite structure, Mg(OH).sub.2, also possess
this "rehydratability" characteristic. It is also known that, if
the crystal size of such materials grows significantly (as it does
with increasingly higher thermal treatment temperatures), then such
"reversibility" is eventually lost. Consequently, the brucite layer
no longer forms upon rehydration. This is the same situation
applicant expected, and in fact observed, for various HTL compounds
made by the teachings of this patent disclosure. Indeed, applicant
found that as temperature increases beyond certain levels, an
increase in a MgO-like material's crystallite size, as well as
alumina and magnesium aluminate (spinel) formation, eventually do
take place. Consequently, for maximum SO.sub.x activity of
applicant's HTL compounds, it is preferred that all the MgO in a
given system remain with the HTL phase as opposed to reacting with
other phases and thereby rendering the MgO "inactive" e.g.,
inactive as a SO.sub.x "pickup agent." Again, this is best achieved
by not using temperatures above about 850.degree. C.
In any case, the heat treated product of Step 1 of applicant's
"activation" process is then subjected to a hydration step. This
hydration step might be termed Step 2 of applicant's activation
procedure. It generally entails mixing the heat treated product of
Step 1 with a quantity of moisture which is such that heat is
evolved from the heat treated precursor material/liquid (e.g.,
water) mixture. The method or manner of hydration to effect
applicant's Step 2 will include, but not limited to such methods as
spraying, impregnating and blunging.
In any case, the heat release produced by this hydration is
indicative of the heat of formation of a HTL compound.
Additionally, this heat release signifies the occurrence of the
chemical reaction which is presumed to be the cause of the greatly
improved physical properties of HTL compounds prepared by the
methods of this patent disclosure. It also should be noted here
that in order to maximize the amount of HTL compound produced by
this hydration step, the amount of water added should be
substantial in quantity (on the order of 30-50 weight percent of
the dry, precursor material). Such amounts of water are required in
order to fully form HTL phases although less water will still
result in a material that exhibits a HTL phase; such a phase will
not, however:, be "pure," i.e., other collapsed HTL phases will be
present (i.e., a MgO-like phase and/or a MgAl solid solution
phase).
Again, depending on the hydration method to be employed, the
previously noted "low temperature," optional drying step also may
be employed in order to render a material having a desired amount
of physical water. And, once again, this low temperature drying
should not exceed about 250.degree. C. because applicant has found
that temperatures in excess of this may result in a premature
release of various interlayer ions, water, crystalline water, or
certain carbonates. In any case, the HTL compound product produced
by applicant's hydration step will possess a crystalline structure
which exhibits an x-ray diffraction pattern that may, and probably
will, reasonably resemble a ICDD "card" for some HTL compound that
has a similar crystalline structure.
In some cases this hydrated product may again be "collapsed" by a
second heat treatment step which might be called Step 3 of
applicant's process (e.g., Step 3 heat treatments at temperatures
ranging from about 300.degree. C. to 850.degree. C. and preferably
at 400.degree. C. to 500.degree. C.) in order to remove its
interstitial water so that the resulting material is better suited
to certain uses such as a SO.sub.x sorbent in a FCC unit. Compounds
created by this third step may be used for any of the purposes for
which the HTL compounds created by applicant's Step 1 and Step 2
materials may be used.
From a broad conceptual point of view, the most fundamental version
of the first embodiment of applicant's invention might be thought
of as being based upon: (1) a "delay" in the production of a
hydrotalcite-like compound end product relative to the point at
which analogous hydrotalcite-like compounds have been made by prior
art production methods, (2) heat treatment (single stage or
multiple stage) of these "not yet" (e.g., with this "not yet"
quality or state being determined by XRD methods) hydrotalcite-like
materials and (3) hydration of the these heat treated materials to
form hydrotalcite-like compounds. Stated another way, it might be
said that the goal of applicant's initial synthesis or chemical
reaction step is to not make as much of a subject, end product, HTL
compound as possible (e.g., not to make as much hydrotalcite as
possible), but rather to make as little of the desired end product
compound, (e.g., to make as little hydrotalcite) as possible.
In any event, applicant's first general process may generally
employ any combination of those HTL compound creating starting
ingredients (e.g., magnesium-containing compounds having less
reactive anions and aluminum-containing compounds having less
reactive anions) and any of those reaction conditions (e.g., short
reaction aging times, neutral pH levels, and ambient temperatures
reaction conditions) that may serve to--and, indeed, strive
to--produce a resulting slurry or precipitate material that does
not exhibit the crystalline structure of the HTL compound that
ultimately will be exhibited by applicant's end product
hydrotalcite-like compound. In fact, the precursor compounds
obtained by the initial chemical reaction step of applicant's first
process may well be entirely amorphous materials having no HTL
structure whatsoever.
In the second embodiment of applicant's invention, however, a
hydrotalcite-like compound is purposely used as the starting
material, or as a precursor compound. That is to say that a
hydrotalcite-like starting material can be purchased
commercially--or it can be synthesized by use of any of the many
methods known to this art and then be employed according to the
teachings of this patent disclosure. In either case, however,
applicant's process calls for heat treatment of the
hydrotalcite-like compound (however obtained) to form a "collapsed"
or "metastable" material. This heat treatment also may be: thought
of as Step 1 of this second embodiment of applicant's invention.
The collapsed or metastable material of this second embodiment is
then hydrated to again form a hydrotalcite-like compound. This
hydration may be thought of as Step 2 of this second embodiment of
applicant's invention. Applicant has found that this "roundabout"
method of producing a hydrotalcite-like compound (from a
hydrotalcite-like compound) is well worth the extra effort because
the resulting hydrotalcite-like compound will be harder and/or more
dense than the original hydrotalcite-like compound from which the
resulting HTL compound was made.
Stated another way, the starting ingredient in the second
embodiment of applicant's invention already will be a rehydratable
hydrotalcite-like compound. This may be evidenced, for example, by
the fact that it already generally displays XRD peaks that resemble
those of a known HTL compound having the same ingredients (e.g., Mg
and Al). In any case, this hydrotalcite-like compound starting
material is then heat treated to convert it into a "collapsed" or
"metastable" compound such as those described in the Miyata
reference, or in the '118 patent. The Step 2, heat treatment of the
second embodiment of this invention can be conducted at a single
preferred temperature (e.g., 450.degree. C.) or at two or more
distinct temperatures in the general temperature range of
300.degree. C. to 850.degree. C. , e.g., at a first, lower
temperature, (e.g., at 300.degree. C.) followed by a second
temperature heat treatment (e.g., at 400.degree. C. to 500.degree.
C.). Here again, however, temperatures greater than about
850.degree. C. are to be avoided in this second embodiment of
applicant's process for the same reasons they were to be avoided in
the first embodiment. For example, if the original synthesis
compound were hydrotalcite, and it experienced a 900.degree. C.
heat treatment temperature for any significant period of time in
the second embodiment of applicant's invention, it too would in
fact be converted it into spinel (MgAl.sub.2 O.sub.4) and, thus,
would be rendered useless for the purposes of practicing this
invention. Here again, any hydrotalcite converted to MgO by such
high temperatures would, however, still be potentially useful in
carrying out functions for applicant's end product materials.
In any case, after the hydrotalcite-like compound of this second
embodiment is heat treated to an extent that it takes on a
"collapsed" or "metastable" form, it can then hydrated (e.g., in a
water system at 20-100.degree. C. for at least 0.1 hours) in the
same manner employed in the first embodiment of this invention to
again form a similar hydrotalcite-like compound. Again, this
"hydrotalcite-like compound--to hydrotalcite-like compound"
production process is not a useless, redundant or roundabout
journey because the hydrotalcite-like compounds resulting from this
second embodiment of applicant's invention will, in fact, have
certain improved physical and/or chemical properties (e.g., greater
density, attrition resistance, catalytic activity, etc.) relative
to those comparable properties possessed by the original
hydrotalcite-like compound from which the resulting or end product
hydrotalcite-like compound was derived. And as in the case of the
first embodiment of this invention, the resulting HTL compound of
this second embodiment can be once again heat treated (this may be
thought of as Step 3 of this second embodiment) at temperatures
ranging from about 300.degree. C. to 850.degree. C. in order to
obtain a yet harder material whose loss of water due to this second
heat treatment may render the resulting material better suited to
certain uses (e.g., as a SO.sub.x absorbent in a FCC unit). That is
to say that Step 3 can be employed to give the resulting material
(here again, a "collapsed" or "metastable" HTL compound-forming
material) improved physical properties relative to those HTL
compounds that are not subjected to this additional heat treatment
process.
The anionic compounds that can be produced by the hereindescribed
processes will most preferably have a chemical structure:
wherein M.sup.2+ and N.sup.3+ are cations, m and n are selected
such that the ratio of m/n is about 1 to about 10, a will have a
value of 1, 2 or 3, A is an anion with charge of -1, -2 or -3, and
b will range between 0 and 10, are highly preferred. The most
preferred elements for "M" in the above structure will be Mg, Ca,
Zn, Mn, Co, Ni, Sr. Ba, Fe and Cu. The most preferred element for
"N" will be Al, Mn, Fe, Co, Ni, Cr, Ga, B, La and Ce. The most
preferred elements for "A" with charge a- will be CO.sub.3.sup.2-,
NO.sub.3.sup.-, SO.sub.4.sup.2-, Cl.sup.- and OH.sup.-, Cr.sup.-,
I.sup.-, SO.sub.4.sup.2-, SiO.sub.3.sup.2-, HPO.sub.3.sup.2-,
MnO.sub.4.sup.2-, HGaO.sub.3.sup.2-, HVO.sub.4.sup.2-.
ClO.sub.4.sup.- and BO.sub.3.sup.2- and mixtures thereof.
Applicant generally has found that HTL compounds made by either of
the two general embodiments of this invention are usually at least
about 10% harder and/or 10% more dense than comparable HTL
compounds made from the same ingredients by prior art production
methods. These physical attribute(s), e.g., of hardness and/or
greater density, makes those catalysts, sorbents, catalyst binders
and ion exchange agents (e.g., water softener agents) made from
applicant's hydrotalcite-like compounds more attrition
resistant--and hence longer lasting--especially in a fluid
catalytic converter ("FCC") environment. Applicant's resulting
compounds also have an improved ability to be regenerated (e.g.,
with respect to their ability to continue to serve as SO.sub.x
sorbents, hydrocarbon cracking (or hydrocarbon forming) catalysts,
ion exchange agents, etc.) after having experienced temperatures
which would permanently deactivate analogous anionic clays (such as
analogous hydrotalcite-like compounds) made by prior art
manufacturing methods. Indeed, these improved physical attributes
can be thought of as even further helping to define applicant's
materials and distinguish them from analogus HTL compounds made by
prior art methods. That is to say that, if applicant's "activation"
procedures (using Steps 1 and 2 or using Steps 1, 2 and 3) produce,
say, a hydrotalcite-like compound exhibiting greater hardness
and/or greater density than a comparable hydrotalcite-like compound
made by other methods, then these qualities may help to distinguish
applicant's "hydrotalcite-like compounds" from those made by prior
art methods.
Because the HTL compounds of this patent disclosure are harder than
HTL compounds made by prior art processes, they present a method
whereby the useful life of a catalyst or sorbent system (such as
those employed in FCC units or fixed bed units) can be extended.
This extension of a catalyst's (or sorbent's) useful life will take
place when the HTL compounds of this patent disclosure are used in
their own right, e.g., as hydrocarbon cracking or forming
catalysts, SO.sub.x sorbents, etc., or when these HTL compounds are
used as binders, matrices, supports, or carriers for other
catalytically active materials (e.g., when they are used as binders
for SO.sub.2.fwdarw.SO.sub.3 oxidant metals).
Thus, using SO.sub.x sorption in a FCC unit used to refine
petroleum as an example, the method of extending the useful life of
an SO.sub.x sorbent (or catalyst) may be expressed in patent claim
language in the following manner:
A method for extending the useful life of a SO.sub.x sorbent system
used in a FCC unit being employed to refine a petroleum feedstock,
said method comprising: employing a HTL compound made by use of a
process of this patent disclosure as a SO.sub.x sorbent system in
the FCC unit and wherein the HTL compound is in the form of a
microspheroidal particle species whose primary function is sorbing
SO.sub.x produced by refining a sulfur-containing petroleum.
Such a HTL compound-containing particle species may further
comprise a binder agent selected group consisting of magnesium
aluminate, hydrous magnesium silicate, magnesium calcium silicate,
calcium silicate, alumina, calcium oxide and calcium aluminate.
Expressed in patent claim language, such a method for extending the
useful life of a SO.sub.x additive system comprised of a
SO.sub.2.fwdarw.SO.sub.3 oxidation catalyst and a SO.sub.3 sorbent
may comprise:
(1) employing the SO.sub.x additive system in the form of at least
two physically distinct particle species wherein a first particle
species contains the SO.sub.2.fwdarw.SO.sub.3 oxidation catalyst
component and carries out a primary function of oxidizing sulfur
dioxide to sulfur trioxide and the second particle species is
physically separate and distinct from the first particle species
and carries out a primary function of sorbing the SO.sub.3 produced
by the SO.sub.2.fwdarw.SO.sub.3 oxidation catalyst;
(2) employing the SO.sub.2.fwdarw.SO.sub.3 oxidation catalyst in
the form of a particle species that comprises: (a) a sulfur
SO.sub.2.fwdarw.SO.sub.3 oxidation catalyst comprised of a metal
selected from the group consisting of cerium, vanadium, platinum,
palladium, rhodium, molybdenum, tungsten, copper, chromium, nickel,
iridium, manganese, cobalt, iron, ytterbium, and uranium; and (b) a
binder made from a material selected from the group of
metal-containing compounds consisting of hydrotalcite-like
compounds, calcium aluminate, aluminum silicate, aluminum titanate,
zinc titanate, aluminum zirconate, magnesium aluminate, alumina
(Al.sub.2 O.sub.3), aluminum hydroxide, an aluminum-containing
metal oxide compound (other than alumina (Al.sub.2 O.sub.3)), clay,
zirconia, titania, silica, clay and clay/phosphate material;
and
(3) using the SO.sub.3 absorbent component in the form of a second
particle that comprises a hydrotalcite-like compound made by use of
an "activation process" of this patent disclosure.
This activation process may involve use of Step 1 and Step 2 (or
Steps 1, 2 and 3) upon a non-hydrotalcite-like starting material or
a hydrotalcite-like starting material. Any of the HTL compounds may
be used in FCC systems wherein the SO.sub.x sorbent particle
species comprises from about 10 to about 90 weight percent of the
overall SO.sub.x additive system (i.e., the SO.sub.x sorbent
particle species and the SO.sub.2.fwdarw.SO.sub.3 oxidant particle
species). Such an overall, SO.sub.x additive system will, in turn,
normally comprise from about 0.5 to about 10.0 weight percent of a
bulk hydrocarbon cracking catalyst (e.g., zeolite) SO.sub.x
additive system.
Next, it should be understood that the HTL compounds made by any of
these methods may be used in any way that the prior art has used
hydrotalcite-like compounds made by any prior art method (e.g.,
they may be used as sorbents and especially SO.sub.x sorbents,
hydrocarbon cracking catalysts, e.g., for use in fixed bed or fluid
bed systems, catalyst carrier or binder materials, anion exchangers
(e.g., water softener agents, etc.) acid residue scavengers,
stabilizers for polymers, medicines, etc.). Applicant's HTL
compounds are, however, particularly useful where the attributes of
physical hardness, toughness, or greater density are especially
desired (e.g., when they are used in FCC units as SO.sub.x
sorbents, catalysts and catalyst binders or carriers).
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a XRD pattern for a 2Mg/1Al ratio HTL precursor
slurry.
FIG. 2 is a XRD pattern for a 2Mg/1Al ratio HTL precursor slurry in
which the slurry has been heat aged at about 80-85.degree. C.
FIG. 3 is a XRD pattern for a 2Mg/1Al ratio HTL precursor slurry in
which the slurry has been heat aged at about 80-85.degree. C. for a
longer duration than the material whose XRD is depicted in FIG.
2.
FIG. 4 is the XRD for a 2Mg/1Al ratio precursor material that has
been heat age treated; and wherein the effects of an amorphous
phase associated with that crystalline phase 2Mg/1Al ratio HTL
precursor have been subtracted from the XRD pattern.
FIG. 5 depicts (via XRD pattern changes) the various phase changes
that take place as a result of the activation process of this
patent disclosure.
FIG. 6 gives the XRD pattern for a 2Mg/1Al ratio HTL phase produced
using applicant's activation process in a case where the starting
2Mg/1Al ratio HTL precursor 'slurry was not heated.
FIG. 7 depicts the XRD for a 2Mg/1Al ratio HTL phase produced by
applicant's activation process using a heated 2Mg/1Al HTL precursor
slurry.
FIG. 8 shows the XRD pattern for a 2Mg/1Al ratio phase material
plus oxidants made by applicant's process.
FIG. 9 shows the XRD for a Mg/Al system activated by applicant's
process and wherein the system has a 5Mg/1Al molar ratio.
FIG. 10 depicts the effects of a one hour, 500.degree. C. heat
treatment on precursor phase with oxidants.
FIG. 11 shows XRD for a 3Mg/1Al/oxidant (Ce, V) system where the
oxidants were added to the precursor slurry after a one hour,
732.degree. C. calcination and wherein the oxidants were added to a
precursor slurry.
FIG. 12 shows XRD for a 3Mg/1Al oxidant (Ce, V) system wherein the
oxidants were added to a precursor slurry and wherein the system
was activated through use of applicant's methods at 732.degree.
C.
FIG. 13 is a TGA/SO.sub.x Sorption and Release trace for a 3Mg/1Al
HTL system prepared by applicant's process.
DETAILED DESCRIPTION OF THE INVENTION
Even though this invention is broadly concerned with anionic clays
in general, it is mostly illustrated through discussions, data and
working examples that focus on those anionic clays known as
hydrotalcite-like ("HTL") compounds. Applicant does this because
(1) HTL compounds are perhaps the most readily formulated anionic
clay compounds, (2) they are the most well studied and reported
anionic clay compounds in the literature and because (3) they are,
in fact, the most preferred compounds for actual practice of
applicant's invention. The crystalline structures of some of the
more preferred forms of HTL compounds for the practice of this
invention reasonably resemble those of: (1) magnesium aluminum
hydroxides, (2) magnesium aluminum hydroxide hydrates and (3)
magnesium aluminum hydroxide carbonate hydrates. They are
preferably made from compositions primarily comprised of (1) a
magnesium-containing compound and (2) an aluminum-containing
compound (e.g., an alumina sol, alumina gels or crystalline
alumina) and, optionally, (3) other ingredients such as metal
oxidants and binder materials commonly used to make certain end
product forms of such HTL compounds (FCC catalysts, SO.sub.x
sorbents, anion exchange pellets, etc.).
Some particularly useful magnesium-based compounds for creating
applicant's HTL compounds will include magnesium hydroxy acetate,
magnesium acetate, magnesium hydroxide, magnesium nitrate,
magnesium hydroxide, magnesium carbonate, magnesium formate,
magnesium chloride, magnesium aluminate, hydrous magnesium silicate
and magnesium calcium silicate.
Some particularly useful aluminum-based compounds for creating
applicant's HTL compounds will include aluminum acetate, aluminum
nitrate, aluminum hydroxide, aluminum carbonate, aluminum formate,
aluminum chloride, hydrous aluminum silicate and aluminum calcium
silicate. In the case of the first embodiment of this invention,
these magnesium-containing compounds and aluminum-containing
compounds should be employed such that the product of their initial
reaction does not produce the HTL compound that will ultimately be
produced by applicant's invention. By way of example only, HTL
compound formation by this initial reaction can be thwarted at this
point in the production process by employing any
synthesis-influencing factor selected from the group consisting of
(1) use of less reactive magnesium-containing and/or less reactive
aluminum-containing compounds (e.g., use of hydroxides instead of
acetate forms of magnesium), (2) use of particulate ingredients
rather than those in true solution, (3) use of relatively short
reaction periods (e.g., less than 0.1 hours), (4) use of "neutral"
pH levels (e.g., 6-8 pH levels) and (5) use of relatively low
temperature reaction conditions (e.g., less than 30.degree.
C.).
Additionally, for use in those applications where other functions
(e.g., oxidation of SO.sub.2.fwdarw.SO.sub.3) is a part of the
proposed end usage of applicant's HTL compounds (e.g., when they
are to be used as FCC catalyst, or SO.sub.x sorbent particles), any
number of well known oxidants may be employed in conjunction with
applicant's HTL compounds. Such oxidants would include, for
example, platinum, those compounds which form oxides of the rare
earth metals, oxides of transition metals, etc. Such oxidants can
also be associated with the HTL compounds of this patent disclosure
by impregnating dried forms of these HTL compounds with solutions
containing ions of such oxidant metals.
Ingredient Proportions
TABLE I illustrates some representative relative concentrations of
several HTL compositions that can be made by the teachings of this
patent disclosure that are especially useful as SO.sub.x sorbent
formulations. They are given in Table I, on a dry oxide basis, both
with and without oxidants.
TABLE I (molar) Mg/Al (ratio) 2/1 3/1 5/1 MgO, w % 61.3 70.4 79.8
Al.sub.2 O.sub.3, w % 38.7 29.6 20.2 MgO, w % 52.1 59.8 67.8
Al.sub.2 O.sub.3, w % 32.9 25.2 17.2 CeO.sub.2, w % 12.0 12.0 12.0
V.sub.2 O.sub.5, w % 3.0 3.0 3.0
It also should be appreciated that the HTL compounds of this patent
disclosure can be used alone (that is to say that they can act
catalytically, as sorbents, etc. and serve as their own binder or
matrix material) or they can be associated with various catalyst
binder or matrix-forming materials that are well known to those
skilled in the catalyst and/or sorbent making arts. Indeed, such
binder or matrix-forming materials may constitute up to about 99
weight percent of an overall catalyst or sorbent material (be it a
microspheroidal particle, pellet, extrudate, etc.) in which the HTL
compounds of this patent disclosure are employed. By way of example
only, such catalyst, SO.sub.x binder or matrix-forming materials
may be magnesia, alumina, aluminum-containing metal oxide
compounds, aluminum hydroxide, clay, zirconia, titania, silica,
clay and/or clay/phosphate materials.
This all goes to say that, even thought the HTL compounds of this
patent disclosure may serve as both an SO sorbent and as its own
binder material in the practice of this invention, applicant's SO
sorbent catalysts (as well as any other solid forms of these HTL
compounds) may, more preferably, comprise at least one HTL compound
made by the processes of this invention and at least one,
chemically different, binder, matrix, support, etc. material for
that HTL compound. For example, a SO.sub.x additive catalyst
intended for use in a FCC unit may be comprised of a
hydrotalcite-like compound supported by, say, a calcium aluminate
binder.
Next it should be again noted that when applicant's HTL compounds
are used as SO sorbent components, or catalysts or anion exchange
agents, etc., they may be so used alone--e.g., as separate and
distinct SO sorbent particles or they may be used with other active
materials which may be present as different particle species or as
components of the particle species that employ the HTL compounds of
this patent disclosure. By way of example only, such particles may
be provided with their own SO.sub.2.fwdarw.SO.sub.3 oxidation
catalyst ingredient(s). Moreover, one or more particle species that
make up applicant's SO sorbent component(s) may be--as an option,
and not a requirement--provided with SO.sub.2.fwdarw.SO.sub.3
oxidation catalysts selected from the group consisting of cerium,
vanadium, platinum, palladium, rhodium, iridium, molybdenum,
tungsten, copper, chromium, nickel, manganese, cobalt, iron,
ytterbium, and uranium. Of these possible SO.sub.2.fwdarw.SO.sub.3
oxidation catalysts, ceria and vanadia have proven to be a
particularly effective SO.sub.2 oxidation catalyst when an SO.sub.2
oxidant is used in conjunction with applicant's HTL compound based,
SO.sub.3 absorbents. It also should be understood, however, that
SO.sub.2.fwdarw.SO.sub.3 oxidation catalysts of this kind also
could be placed upon an entirely separate and distinct particle
species that is admixed with those particles that are made with
applicant's HTL compounds.
Preparation and Processing
As previously discussed, the first embodiment of this invention,
among other things, requires that an amorphous and/or
non-crystalline HTL phase be present at the end of the slurry or
precipitate preparation step. A diffraction pattern for a
representative material of this kind is shown in FIG. 1. FIGS. 2-3
show the effects of "low temperature" (i.e., less than about
100.degree. C.) heat aging the material whose XRD pattern is shown
in FIG. 1. These figures show the presence of significant amorphous
phases, as well as non-HTL crystalline phases. The particular
materials associated with these figures were prepared using a
2Mg/1Al molar ratio. In one case, illustrated in FIG. 1, the slurry
was not heat aged, while the material whose XRD pattern is shown in
FIGS. 2 and 3 was heat aged at about 80-85.degree. C. FIGS. 2 and 3
show that upon being subjected to such low temperature heating, a
new crystalline phase nucleates and grows with increasing aging
time. FIG. 4 shows the crystalline portion of the phase that was
shown in FIG. 2. That is to say that the effects of the presence of
the amorphous material that are present in FIG. 2 are "subtracted
out" of the XRD pattern shown in FIG. 4.
FIG. 5 shows the changes in crystal structure at various steps in
applicant's "activation" process. The top two curves in this plot
(respectively labeled "2Mg/1Al Precursor before heat aging" and
"2Mg/1Al Precursor after heat aging") already have been discussed
as part of the previous discussion of FIGS. 1 to 4. The trace in
FIG. 5 labeled "heat treated" is representative of the observed
phases of HTL structures following Step 1 of applicant's activation
process. The trace labeled "heat treat+hydrate (activated HTL)"
depicts the results of Step 2 of applicant's activation process.
Clearly, an HTL structure has been created. This is evidenced by
the presence of all major peaks of an HTL compound, including peaks
at about 11.271 degrees, 22.700 degrees and 34.358 degrees
manifesting their presence. It also should be noted that FIG. 5
includes the effects of the CeO.sub.2 component that was added
during the synthesis reaction and whose most prominent peaks
manifest themselves at 28.555 degrees, 47.479 degrees and 56.335
degrees.
FIGS. 6 and 7 plot the XRD pattern for a 2Mg/1Al HTL compound that
is produced using applicant's activation process. The compound that
generated FIG. 6 was derived from an un-heated slurry, while that
for FIG. 7 was heat aged. The "stick diagram" (vertical lines of
different heights at the appropriate 2.theta. positions) for the
"best matching" ICDD card is superimposed on each of these two
plots. In this case the "best match" was with ICDD "card" 35-965
for Mg.sub.6 Al.sub.2 (OH).sub.18 -4.5H.sub.2 O. It also should be
emphasized here that certain other ICDD cards (e.g., ICDD card
22-700 for hydrotalcite) reasonably "matched" the peak positions
and intensities to give reasonably close correlations, but this
particular HTL compound has 2.theta. peak positions that are nearly
identical to those of the 35-965 card. This HTL compound also
displayed XRD intensities which had the fewest inconsistencies
relative to those of the several candidate cards that were
considered. The lattice parameters of both the aged and non-aged
slurry example are compared in TABLE II with the "best matching"
card, namely, ICDD card 35-965.
TABLE II ICDD Card 2Mg/1A1 HTL 2Mg/1A1 HTL 35-965 (not aged) (aged
slurry) a, Angstrom 3.054 3.057 3.060 c, Angstrom 23.40 23.05 23.08
alpha, degrees 90 90 90 beta, degrees 90 90 90 gamma, degrees 120
120 120
It can be seen that the lattice parameter, "a," of applicant's
2Mg/1Al HTL compound is nearly identical to that of the card, while
lattice parameter "c" is substantially lower. Applicant believes
that this signifies that the amount of Al.sup.3+ substituted into
the brucite-like structure is nearly identical to that of the
35-965 card material, while the variation in lattice parameter c is
due to the nature and amount of interlayer water and
charge-balancing anions located in the interlayer.
FIG. 8 shows the XRD patterns for the same 2Mg/1Al HTL compound
used to generate FIGS. 6 and 7, except that 12 weight percent
CeO.sub.2 and 3 weight percent V.sub.2 O.sub.5 components are
present by virtue of cerium-containing compound (e.g., cerium
nitrate) being added to the slurry formulation after reacting the
magnesium and aluminum containing components together. It also
should be noted that, with the exception of the effects of the
CeO.sub.2 present (ICDD Card 34-394) in this system, the pattern is
very similar to those samples containing no oxidants (again, see
FIGS. 6 and 7).
The following TABLE III compares XRD patterns for HTL compounds
with, and without, oxidants as compared to the patterns of the
"most closely matching" ICDD card. This comparison shows that the
presence of the oxidants in no way affects the structure of the HTL
compound.
TABLE III ICDD Card no with oxidants 35-965 oxidants CeO.sub.2 and
V.sub.2 O.sub.5 a, Angstrom 3.054 3.057 3.046 c, Angstrom 23.40
23.05 23.07 alpha, degrees 90 90 90 beta, degrees 90 90 90 gamma,
degrees 120 120 120
Thus, based upon these and other findings, applicant has concluded
that, within a reasonable experimental error allowance for this
kind of analysis, no appreciable difference in crystal structure
can be observed between HTL compounds associated with CeO.sub.2 and
V.sub.2 O.sub.5 oxidants and those without such oxidants.
Diffraction patterns showing the effect of a higher Mg/Al ratio
(i.e., 5:1) in the HTL structural formation are shown in FIGS. 9.
In addition to the HTL compound and oxidant CeO.sub.2, a small
amount of magnesium hydroxide (ICDD Card 7-239) was observed in the
pattern shown in FIG. 10. This result is consistent with results
published in the literature in that the maximum HTL formation has
been determined by other workers in this art (e.g., Miyata) to be
in the Mg/Al ratio range of 2-4. Since the sample that generated
FIG. 10 was prepared at a 5Mg/1Al ratio, the amount of magnesium
ions present in such a system exceeded the limit of their
solubility in the brucite layer--hence a magnesium hydroxide phase
was formed and manifested itself in this way.
FIG. 10 shows the crystal structure present for HTL precursors
materials having differing Mg/Al ratios just prior to Step 2 of
applicant's activation process. of particular interest here are the
"shoulders" on the 43 degree and 62 degree "MgO-like" peaks of
these diffractograms. It can be seen that, as the Mg/Al ratio
increases from 2:1 to 5:1, the magnitude of these peaks diminishes
to a level where they become undetectable. This is indicative of a
metastable alumina phase, with or without a small amount of
magnesium oxide dissolved in the lattice. Additionally, this result
shows that alumina is present, primarily within the lattice of the
MgO, and hence the term "MgO-like" compounds also might be applied
to those HTL compounds that have undergone applicant's Step 2 heat
treatment--but no hydration. The metastable alumina phase is a
direct corollary to the 5Mg/1Al material previously discussed
wherein the presence of "too many" Mg ions resulted in an excess
that manifested itself as a magnesium hydroxide phase. In this
case, "too low" a Mg/Al ratio results in an excess of alumina which
can be regarded as a slightly magnesia-rich alumina phase. This
observation has been made in the literature as well; see, for
example, Gastuche et al, Mixed Magnesium-Aluminum Hydroxides, Clay
Minerals 7, 7 (1967), particularly noting FIG. 1 therein. See also
the previously noted Miyata reference, (and especially page 52
thereof).
Thus, for maximum HTL formation by applicant's processes,
hydrotalcite-like compounds having a Mg/Al ratio in the 2-4 range
are highly preferred. When the Mg/Al ratio drops below 2, a HTL
structure can result, but it will be mixed with alumina and or a
magnesium-aluminum solid solution phase. The lattice parameter, a,
of such a system, however, generally, will remain unchanged at
about 3.04 Angstroms. In a system having a Mg/Al ratio in the range
of 2-4, the lattice parameter, a, will increases with a linear
relationship toward an end-point associated with magnesium
hydroxide of 3.14-3.15 Angstroms. Above a Mg/Al ratio of 4, the
lattice parameter continues to increase further, but magnesium
hydroxide will accompany the HTL phase formation. See again, for
example, the previously cited Miyata reference and the Gastuche et
al. reference (and especially FIG. 1, on pg 182 thereof).
The effects of increased temperature of applicant's activation
process with respect to crystal structure was also studied. This
study verified the literature's pronouncements with respect to the
temperature at which spinel is formed from hydrotalcite. For
example, applicant subjected a commercially available hydrotalcite
compound to such a rising temperature regime in order to verify the
temperature at which spinel is formed from hydrotalcite. The
commercially available hydrotalcite was Alcoa's HTC-30.RTM. product
(which has a 3:1 Mg/Al molar ratio and is therefore well suited to
use in the second embodiment of applicant's invention), and it was
subjected to temperatures that ranged from 250.degree. C. to
1200.degree. C. This test showed MgO-like phase formation
commencing at 400.degree. C. and spinel formation commencing at
900.degree. C.
The results of some other analogous heat treatments, carried out at
higher heat treatment temperatures, is presented in FIGS. 11 and
12. In these increased temperature studies, a 732.degree. C.
temperature was used for one hour as the heat treatment aspect of
applicant's overall "activation" step since the literature states
that this is near the upper-end of preferred temperature for
maximum HTL phase formation. In any case, no appreciable
differences in structure are noted beyond those already noted for
lower temperature activations (e.g., at 450-500.degree. C.)
TGA-SO.sub.x Testing of Sorbents
A modified Thermal Gravimetric Analysis (TGA) technique is used by
many laboratories worldwide to evaluate the relative SO.sub.x
sorbent performance of different compositions. This modified
technique employs two tests, which are carried out at different
temperatures. The first test is a SO.sub.x "pickup." In this aspect
of the TGA test, a furnace is ramped up to about 700.degree. C. in
an inert gas and allowed to equilibrate. A gas mixture containing
SO.sub.2 and O.sub.2 is then introduced into the reactor for some
duration. It should be understood that two distinct reactions are
simultaneously occurring at this point: Oxidation of
SO.sub.2.fwdarw.SO.sub.3 and a subsequent reaction of the SO.sub.3
thus formed with MgO to form MgSO.sub.4. Typically, the reaction is
allowed to continue until the sample is saturated (meaning all the
possible MgO is reacted to form the sulfate). The second aspect of
the TGA is to regenerate the sorbent. This is achieved through use
of a lower temperature (typically 590.degree. C.) and a reducing
atmosphere (typically H.sub.2), so that the sorbent being studied
releases the sorbed SO.sub.x as H.sub.2 S. The TGA-SO.sub.x plot
for one cycle of such a test on one of applicant's HTL compounds is
shown in FIG. 13.
Methods for Forming HTL Compositions which are Particularly
Resistant to Mechanical Stress
The HTL compounds of this invention can be formed into various
shapes (particles, microspheroidal particles, extrudates, pellets)
which are harder and more dense than HTL compounds made by prior
art processes. These qualities make applicant's HTL compounds more
useful for certain applications e.g., catalysts, sorbents in
general (and SO.sub.x sorbents in particular), ion exchange pellets
(e.g., for water softeners). If made according to the teachings of
this patent disclosure, such physical forms will display greater
resistance to wear, attrition, or impact, as well as improvement
(i.e., increase) in the bulk density of the HTL compounds formed by
applicant's methods.
The following Table IV summarizes improvements in two physical
properties (i.e., attrition index and apparent bulk density
("ABD")) for various samples that were spray dried into particle
forms and activated according to the teachings of this patent
disclosure. This activation method would also be applicable to
other physical forms of such HTL compounds, e.g., extrudates,
pellets or beads.
TABLE IV Attrition Index HTL Composition (ASTM) *ABD (g/cc) 2Mg/1A1
(Step 1 Activation) 3.9 0.39 2Mg/1A1 (Step 2 Activation) 0.54 0.96
5Mg/1A1 (Step 1 Activation) 15 0.36 5Mg/1A1 (Step 2 Activation)
0.65 0.75 *Apparent Bulk Density
The 2Mg/1Al sample described in Table IV also was subjected to an
additional heat treatment step at 732.degree. C. /1 hr. This
additional heat treatment has been described as an optional, "Step
3" in previous parts of this patent disclosure. This additional
heating was performed to show that applicant's "activation" was of
irreversible nature, meaning the physical properties do not revert
to the original activation values. Therefore, applicant considers
the products of this "activation" to be new compositions of matter.
In any case, the results of this Step 3 process are shown in Table
V.
TABLE V Attrition Index HTL composition (ASTM) ABD (g/cc) 2Mg/1A1
(Step 1 Activation) 3.9 0.96 2Mg/1A1 (Step 2 Activation) 0.54 0.96
2Mg/1A1 (Additional heat to 0.81 0.80 732C/1 hr.)
Applicability of Activation Process Toward HTL Compounds which
Crystallize with HTL Structure During Slurry Synthesis
The aforementioned activation process (i.e., heat treatment
followed by hydration) can be applied to HTL compounds that are
used as starting materials in the second embodiment of applicant's
invention. That is to say that a HTL compound can be heat treated
to form a "collapsed" or "metastable" material that can be
rehydrated in the same manner that the heat treated material of the
first embodiment of applicant's invention was hydrated. If so heat
treated, the hydration process of the second embodiment of this
invention will result in formation of a HTL phase. Here again,
applicant's activation process improves the physical
characteristics of the HTL materials produced by said process.
Again, these improvements include, but are not limited to, improved
mechanical strength and density of the formed shapes (e.g., FCC
particles, fixed bed pellets, anion exchange beads, etc.) relative
to comparable compounds that do not experience applicant's
activation process. It also should be noted that, for those
materials which form HTL compounds from HTL starting materials
(i.e., the second embodiment of applicant's invention), the
resulting HTL phase may or may not be exactly identical to the
starting HTL phase (in terms of exact identity of peak position and
intensity), but which will nonetheless display clearly identifiable
HTL compound peaks and possess the above-noted improved physical
characteristics.
To show this advance, an example is given of a HTL containing
SO.sub.x sorbent (marketed by Akzo Nobel under the trade name
"KDESOX.RTM.") that was subjected to applicant's activation
process. The following TABLE VI summarizes the physical
characteristics of the HTL-containing composition, before and after
Applicant's activation process.
TABLE VI KDESOX KDESOX HTL Composition (as received) "Activated"
Attrition Index, ASTM 1.8 0.77 Bulk Density, g/cc 0.81 0.97
Thus, the physical properties (shown here as attrition index and
bulk density) of a commercial available HTL compound made into FCC
particles can be improved markedly by subjecting them to
applicant's Activation process.
While this invention has been described with respect to various
theories, specific examples and a spirit which is committed to the
concept of the use of an "activation process" that is based upon
heat treatment and hydration of collapsed, HTL-forming, compounds,
the full scope of this invention relates to such activation of
anionic clays in general; hence the full scope of this invention
should be regarded as being limited only by the claims that
follow.
* * * * *